Abstract
Genioglossus is the largest upper airway dilator and its dilatory movement can be measured non-invasively with magnetic resonance imaging and ultrasound. The present study used a novel ultrasound method to assess genioglossus movement in conditions in which ventilatory drive or respiratory mechanics were changed.MethodsTwenty healthy subjects (10 males, age 28±5 years [mean ± SD]) lay supine, awake, with the head in a neutral position. Ventilation was monitored with inductance bands. Real-time B-mode ultrasound movies were analysed. We measured genioglossus motion (i) during spontaneous breathing, voluntary targeted breathing (normal tidal volume Vt), and voluntary hyperpnoea (at 1.5Vt and 2 Vt); (ii) during inspiratory flow resistive loading; (iii) with changes in end-expiratory lung volume (EELV).ResultsAverage peak inspiratory displacement of the infero-posterior region of genioglossus was 0.89±0.56 mm; 1.02±0.88 mm; 1.27±0.70 mm respectively for voluntary Vt, and during voluntary hyperpnoea at 1.5Vt and 2Vt. A change in genioglossus motion was observed with increased Vt. During increasing inspiratory resistive loading, the genioglossus displaced less anteriorly (p = 0.005) but more inferiorly (p = 0.027). When lung volume was altered, no significant changes in genioglossus movement were observed (p = 0.115).ConclusionIn healthy subjects, we observed non-uniform heterogeneous inspiratory motion within the inferoposterior part of genioglossus during spontaneous quiet breathing with mean peak displacement between 0.5–2 mm, with more displacement in the posterior region than the anterior. This regional heterogeneity disappeared during voluntary targeted breathing. This may be due to different neural drive to genioglossus during voluntary breathing. During inspiratory resistive loading, the observed genioglossus motion may serve to maintain upper airway patency by balancing intraluminal negative pressure with positive pressure generated by upper airway dilatory muscles. In contrast, changes in EELV were not accompanied by major changes in genioglossus motion.
Highlights
The human upper airway is important in many voluntary and involuntary tasks such as swallowing, speech and breathing
A change in genioglossus motion was observed with increased voluntary tidal breathing” (Vt)
Influence of respiratory mechanics and drive on genioglossus movement under ultrasound imaging airway patency by balancing intraluminal negative pressure with positive pressure generated by upper airway dilatory muscles
Summary
The human upper airway is important in many voluntary and involuntary tasks such as swallowing, speech and breathing. Patency of the upper airway requires a dynamic coordinated system that can rapidly change dilator muscle activity to counterbalance pressures that act to collapse it [1, 2]. The system is influenced by active moment-to-moment changes such as pressures generated as a result of neural drive to dilator and other upper airway muscles [10]. Genioglossus electromyographic (EMG) activity has been reported to increase during inspiratory flow-resistive loading [18, 19]. Fogel and colleagues found that phasic genioglossus EMG increases with increasing intrapharynegal negative pressure during passive ventilation, and inspiratory resistive loading [20]. During voluntary hyperventilation in the supine position, genioglossus EMG increases when compared to tidal breathing at rest [21, 22]
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